﻿using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Diagnostics;
using System.Linq;
using System.Reactive.Linq;
using System.Threading;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using CommunityToolkit.Mvvm.Messaging;
using MoreLinq;
using Nito.AsyncEx;
using Serilog;
using Wino.Core.Domain;
using Wino.Core.Domain.Entities.Mail;
using Wino.Core.Domain.Entities.Shared;
using Wino.Core.Domain.Enums;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Domain.Models.Folders;
using Wino.Core.Domain.Models.MailItem;
using Wino.Core.Domain.Models.Menus;
using Wino.Core.Domain.Models.Reader;
using Wino.Core.Domain.Models.Server;
using Wino.Core.Domain.Models.Synchronization;
using Wino.Mail.ViewModels.Collections;
using Wino.Mail.ViewModels.Data;
using Wino.Mail.ViewModels.Messages;
using Wino.Messaging.Client.Mails;
using Wino.Messaging.Server;
using Wino.Messaging.UI;

namespace Wino.Mail.ViewModels;

public partial class MailListPageViewModel : MailBaseViewModel,
    IRecipient<MailItemNavigationRequested>,
    IRecipient<ActiveMailFolderChangedEvent>,
    IRecipient<MailItemSelectedEvent>,
    IRecipient<MailItemSelectionRemovedEvent>,
    IRecipient<AccountSynchronizationCompleted>,
    IRecipient<NewMailSynchronizationRequested>,
    IRecipient<AccountSynchronizerStateChanged>,
    IRecipient<AccountCacheResetMessage>,
    IRecipient<ThumbnailAdded>
{
    private bool isChangingFolder = false;

    private Guid? trackingSynchronizationId = null;
    private int completedTrackingSynchronizationCount = 0;

    /* [Bug] Unread folder reads All emails automatically with setting "Mark as Read: When Selected" enabled 
     * https://github.com/bkaankose/Wino-Mail/issues/162
     * We store the UniqueIds of the mails that are marked as read in Gmail Unread folder
     * to prevent them from being removed from the list when they are marked as read.
     */

    private readonly HashSet<Guid> gmailUnreadFolderMarkedAsReadUniqueIds = [];

    private IObservable<System.Reactive.EventPattern<NotifyCollectionChangedEventArgs>> selectionChangedObservable = null;

    public WinoMailCollection MailCollection { get; }

    public ObservableCollection<MailItemViewModel> SelectedItems { get; set; } = [];
    public ObservableCollection<FolderPivotViewModel> PivotFolders { get; set; } = [];
    public ObservableCollection<MailOperationMenuItem> ActionItems { get; set; } = [];

    private readonly SemaphoreSlim listManipulationSemepahore = new SemaphoreSlim(1);
    private CancellationTokenSource listManipulationCancellationTokenSource = new CancellationTokenSource();

    public INavigationService NavigationService { get; }
    public IStatePersistanceService StatePersistenceService { get; }
    public IPreferencesService PreferencesService { get; }
    public IThemeService ThemeService { get; }

    private readonly IAccountService _accountService;
    private readonly IMailDialogService _mailDialogService;
    private readonly IMailService _mailService;
    private readonly IFolderService _folderService;
    private readonly IThreadingStrategyProvider _threadingStrategyProvider;
    private readonly IContextMenuItemService _contextMenuItemService;
    private readonly IWinoRequestDelegator _winoRequestDelegator;
    private readonly IKeyPressService _keyPressService;
    private readonly IWinoLogger _winoLogger;
    private readonly IWinoServerConnectionManager _winoServerConnectionManager;
    private MailItemViewModel _activeMailItem;

    public List<SortingOption> SortingOptions { get; } =
    [
        new(Translator.SortingOption_Date, SortingOptionType.ReceiveDate),
        new(Translator.SortingOption_Name, SortingOptionType.Sender),
    ];

    public List<FilterOption> FilterOptions { get; } =
    [
        new (Translator.FilteringOption_All, FilterOptionType.All),
        new (Translator.FilteringOption_Unread, FilterOptionType.Unread),
        new (Translator.FilteringOption_Flagged, FilterOptionType.Flagged),
        new (Translator.FilteringOption_Files, FilterOptionType.Files)
    ];

    private FolderPivotViewModel _selectedFolderPivot;

    [ObservableProperty]
    private bool isMultiSelectionModeEnabled;

    [ObservableProperty]
    public partial string SearchQuery { get; set; }

    [ObservableProperty]
    private FilterOption _selectedFilterOption;
    private SortingOption _selectedSortingOption;

    // Indicates state when folder is initializing. It can happen after folder navigation, search or filter change applied or loading more items.
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(IsEmpty))]
    [NotifyPropertyChangedFor(nameof(IsFolderEmpty))]
    [NotifyPropertyChangedFor(nameof(IsProgressRing))]
    private bool isInitializingFolder;

    [ObservableProperty]
    private InfoBarMessageType barSeverity;

    [ObservableProperty]
    private string barMessage;

    [ObservableProperty]
    private double mailListLength = 420;

    [ObservableProperty]
    private double maxMailListLength = 1200;

    [ObservableProperty]
    private string barTitle;

    [ObservableProperty]
    private bool isBarOpen;

    /// <summary>
    /// Current folder that is being represented from the menu.
    /// </summary>
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(CanSynchronize))]
    [NotifyPropertyChangedFor(nameof(IsFolderSynchronizationEnabled))]
    private IBaseFolderMenuItem activeFolder;

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(CanSynchronize))]
    private bool isAccountSynchronizerInSynchronization;

    public MailListPageViewModel(IMailDialogService dialogService,
                                 INavigationService navigationService,
                                 IAccountService accountService,
                                 IMailDialogService mailDialogService,
                                 IMailService mailService,
                                 IStatePersistanceService statePersistenceService,
                                 IFolderService folderService,
                                 IThreadingStrategyProvider threadingStrategyProvider,
                                 IContextMenuItemService contextMenuItemService,
                                 IWinoRequestDelegator winoRequestDelegator,
                                 IKeyPressService keyPressService,
                                 IPreferencesService preferencesService,
                                 IThemeService themeService,
                                 IWinoLogger winoLogger,
                                 IWinoServerConnectionManager winoServerConnectionManager)
    {
        MailCollection = new WinoMailCollection(threadingStrategyProvider);
        PreferencesService = preferencesService;
        ThemeService = themeService;
        _winoLogger = winoLogger;
        _winoServerConnectionManager = winoServerConnectionManager;
        StatePersistenceService = statePersistenceService;
        NavigationService = navigationService;
        _accountService = accountService;
        _mailDialogService = mailDialogService;
        _mailService = mailService;
        _folderService = folderService;
        _threadingStrategyProvider = threadingStrategyProvider;
        _contextMenuItemService = contextMenuItemService;
        _winoRequestDelegator = winoRequestDelegator;
        _keyPressService = keyPressService;

        SelectedFilterOption = FilterOptions[0];
        SelectedSortingOption = SortingOptions[0];

        mailListLength = statePersistenceService.MailListPaneLength;

        selectionChangedObservable = Observable.FromEventPattern<NotifyCollectionChangedEventArgs>(SelectedItems, nameof(SelectedItems.CollectionChanged));
        selectionChangedObservable
            .Throttle(TimeSpan.FromMilliseconds(100))
            .Subscribe(async a =>
            {
                await ExecuteUIThread(() => { SelectedItemCollectionUpdated(a.EventArgs); });
            });

        MailCollection.MailItemRemoved += (c, removedItem) =>
        {
            if (removedItem is ThreadMailItemViewModel removedThreadViewModelItem)
            {
                foreach (var viewModel in removedThreadViewModelItem.ThreadItems.Cast<MailItemViewModel>())
                {
                    if (SelectedItems.Contains(viewModel))
                    {
                        SelectedItems.Remove(viewModel);
                    }
                }
            }
            else if (removedItem is MailItemViewModel removedMailItemViewModel && SelectedItems.Contains(removedMailItemViewModel))
            {
                SelectedItems.Remove(removedMailItemViewModel);
            }
        };
    }

    private void SetupTopBarActions()
    {
        ActionItems.Clear();
        var actions = GetAvailableMailActions(SelectedItems);
        actions.ForEach(a => ActionItems.Add(a));
    }

    #region Properties

    /// <summary>
    /// Selected internal folder. This can be either folder's own name or Focused-Other.
    /// </summary>
    public FolderPivotViewModel SelectedFolderPivot
    {
        get => _selectedFolderPivot;
        set
        {
            if (_selectedFolderPivot != null)
                _selectedFolderPivot.SelectedItemCount = 0;

            SetProperty(ref _selectedFolderPivot, value);
        }
    }

    /// <summary>
    /// Selected sorting option.
    /// </summary>
    public SortingOption SelectedSortingOption
    {
        get => _selectedSortingOption;
        set
        {
            if (SetProperty(ref _selectedSortingOption, value))
            {
                if (value != null && MailCollection != null)
                {
                    MailCollection.SortingType = value.Type;
                }
            }
        }
    }

    public bool CanSynchronize => !IsAccountSynchronizerInSynchronization && IsFolderSynchronizationEnabled;
    public bool IsFolderSynchronizationEnabled => ActiveFolder?.IsSynchronizationEnabled ?? false;
    public int SelectedItemCount => SelectedItems.Count;
    public bool HasMultipleItemSelections => SelectedItemCount > 1;
    public bool HasSingleItemSelection => SelectedItemCount == 1;
    public bool HasSelectedItems => SelectedItems.Any();
    public bool IsArchiveSpecialFolder => ActiveFolder?.SpecialFolderType == SpecialFolderType.Archive;

    public string SelectedMessageText => HasSelectedItems ? string.Format(Translator.MailsSelected, SelectedItemCount) : Translator.NoMailSelected;

    /// <summary>
    /// Indicates current state of the mail list. Doesn't matter it's loading or no.
    /// </summary>
    public bool IsEmpty => MailCollection.Count == 0;

    /// <summary>
    /// Progress ring only should be visible when the folder is initializing and there are no items. We don't need to show it when there are items.
    /// </summary>
    public bool IsProgressRing => IsInitializingFolder && IsEmpty;
    public bool IsFolderEmpty => !IsInitializingFolder && IsEmpty;

    public bool HasNoOnlineSearchResult { get; private set; }

    [ObservableProperty]
    public partial bool IsInSearchMode { get; set; }

    [ObservableProperty]
    public partial bool IsOnlineSearchButtonVisible { get; set; }

    [ObservableProperty]
    public partial bool IsOnlineSearchEnabled { get; set; }

    [ObservableProperty]
    public partial bool AreSearchResultsOnline { get; set; }

    #endregion

    private async void ActiveMailItemChanged(MailItemViewModel selectedMailItemViewModel)
    {
        if (_activeMailItem == selectedMailItemViewModel) return;

        // Don't update active mail item if Ctrl key is pressed or multi selection is enabled.
        // User is probably trying to select multiple items.
        // This is not the same behavior in Windows Mail,
        // but it's a trash behavior.

        var isCtrlKeyPressed = _keyPressService.IsCtrlKeyPressed();

        bool isMultiSelecting = isCtrlKeyPressed || IsMultiSelectionModeEnabled;

        if (isMultiSelecting && StatePersistenceService.IsReaderNarrowed)
        {
            return;
        }

        _activeMailItem = selectedMailItemViewModel;

        Messenger.Send(new ActiveMailItemChangedEvent(_activeMailItem));

        if (_activeMailItem == null || _activeMailItem.IsRead) return;

        // Automatically set mark as read or not based on preferences.

        var markAsPreference = PreferencesService.MarkAsPreference;

        if (markAsPreference == MailMarkAsOption.WhenSelected)
        {
            var operation = MailOperation.MarkAsRead;
            var package = new MailOperationPreperationRequest(operation, _activeMailItem.MailCopy);

            if (ActiveFolder?.SpecialFolderType == SpecialFolderType.Unread &&
                !gmailUnreadFolderMarkedAsReadUniqueIds.Contains(_activeMailItem.UniqueId))
            {
                gmailUnreadFolderMarkedAsReadUniqueIds.Add(_activeMailItem.UniqueId);
            }

            await ExecuteMailOperationAsync(package);
        }
        else if (markAsPreference == MailMarkAsOption.AfterDelay && PreferencesService.MarkAsDelay >= 0)
        {
            // TODO: Start a timer then queue.
        }
    }

    public void NotifyItemSelected()
    {
        OnPropertyChanged(nameof(SelectedMessageText));
        OnPropertyChanged(nameof(HasSingleItemSelection));
        OnPropertyChanged(nameof(HasSelectedItems));
        OnPropertyChanged(nameof(SelectedItemCount));
        OnPropertyChanged(nameof(HasMultipleItemSelections));

        if (SelectedFolderPivot != null)
            SelectedFolderPivot.SelectedItemCount = SelectedItemCount;
    }

    private void NotifyItemFoundState()
    {
        OnPropertyChanged(nameof(IsEmpty));
        OnPropertyChanged(nameof(IsFolderEmpty));
    }

    protected override void OnDispatcherAssigned()
    {
        base.OnDispatcherAssigned();

        MailCollection.CoreDispatcher = Dispatcher;
    }

    private async void UpdateBarMessage(InfoBarMessageType severity, string title, string message)
    {
        await ExecuteUIThread(() =>
        {
            BarSeverity = severity;
            BarTitle = title;
            BarMessage = message;

            IsBarOpen = true;
        });
    }

    private void SelectedItemCollectionUpdated(NotifyCollectionChangedEventArgs e)
    {
        if (SelectedItems.Count == 1)
        {
            ActiveMailItemChanged(SelectedItems[0]);
        }
        else
        {
            // At this point, either we don't have any item selected 
            // or we have multiple item selected. In either case
            // there should be no active item.

            ActiveMailItemChanged(null);
        }

        NotifyItemSelected();

        SetupTopBarActions();
    }

    private async Task UpdateFolderPivotsAsync()
    {
        if (ActiveFolder == null) return;

        PivotFolders.Clear();
        SelectedFolderPivot = null;

        if (IsInSearchMode)
        {
            var isFocused = SelectedFolderPivot?.IsFocused;

            PivotFolders.Add(new FolderPivotViewModel(Translator.SearchPivotName, isFocused));
        }
        else
        {
            // Merged folders don't support focused feature.

            if (ActiveFolder is IMergedAccountFolderMenuItem)
            {
                PivotFolders.Add(new FolderPivotViewModel(ActiveFolder.FolderName, null));
            }
            else if (ActiveFolder is IFolderMenuItem singleFolderMenuItem)
            {
                var parentAccount = singleFolderMenuItem.ParentAccount;

                bool isFocusedInboxEnabled = await _accountService.IsAccountFocusedEnabledAsync(parentAccount.Id);
                bool isInboxFolder = ActiveFolder.SpecialFolderType == SpecialFolderType.Inbox;

                // Folder supports Focused - Other
                if (isInboxFolder && isFocusedInboxEnabled)
                {
                    // Can be passed as empty string. Focused - Other will be used regardless.
                    var focusedItem = new FolderPivotViewModel(string.Empty, true);
                    var otherItem = new FolderPivotViewModel(string.Empty, false);

                    PivotFolders.Add(focusedItem);
                    PivotFolders.Add(otherItem);
                }
                else
                {
                    // If the account and folder doesn't support focused feature, just add itself.
                    PivotFolders.Add(new FolderPivotViewModel(singleFolderMenuItem.FolderName, null));
                }
            }
        }



        // This will trigger refresh.
        SelectedFolderPivot = PivotFolders.FirstOrDefault();
    }

    #region Commands

    [RelayCommand]
    public Task ExecuteHoverAction(MailOperationPreperationRequest request) => ExecuteMailOperationAsync(request);

    [RelayCommand]
    private async Task ExecuteTopBarAction(MailOperationMenuItem menuItem)
    {
        if (menuItem == null || !SelectedItems.Any()) return;

        await HandleMailOperation(menuItem.Operation, SelectedItems);
    }

    /// <summary>
    /// Executes the requested mail operation for currently selected items.
    /// </summary>
    /// <param name="operation">Action to execute for selected items.</param>
    [RelayCommand]
    private async Task ExecuteMailOperation(MailOperation mailOperation)
    {
        if (!SelectedItems.Any()) return;

        await HandleMailOperation(mailOperation, SelectedItems);
    }

    private async Task HandleMailOperation(MailOperation mailOperation, IEnumerable<MailItemViewModel> mailItems)
    {
        if (!mailItems.Any()) return;

        var package = new MailOperationPreperationRequest(mailOperation, mailItems.Select(a => a.MailCopy));

        await ExecuteMailOperationAsync(package);
    }

    /// <summary>
    /// Sens a new message to synchronize current folder.
    /// </summary>
    [RelayCommand]
    private void SyncFolder()
    {
        if (!CanSynchronize) return;

        // Only synchronize listed folders.

        // When doing linked inbox sync, we need to save the sync id to report progress back only once.
        // Otherwise, we will report progress for each folder and that's what we don't want.

        trackingSynchronizationId = Guid.NewGuid();
        completedTrackingSynchronizationCount = 0;

        foreach (var folder in ActiveFolder.HandlingFolders)
        {
            var options = new MailSynchronizationOptions()
            {
                AccountId = folder.MailAccountId,
                Type = MailSynchronizationType.CustomFolders,
                SynchronizationFolderIds = [folder.Id],
                GroupedSynchronizationTrackingId = trackingSynchronizationId
            };

            Messenger.Send(new NewMailSynchronizationRequested(options, SynchronizationSource.Client));
        }
    }

    [RelayCommand]
    private async Task SelectedPivotChanged()
    {
        if (isChangingFolder) return;

        await InitializeFolderAsync();
    }

    [RelayCommand]
    private async Task SelectedSortingChanged(SortingOption option)
    {
        SelectedSortingOption = option;

        if (isChangingFolder) return;

        await InitializeFolderAsync();
    }

    [RelayCommand]
    private async Task SelectedFilterChanged(FilterOption option)
    {
        SelectedFilterOption = option;

        if (isChangingFolder) return;

        await InitializeFolderAsync();
    }

    [RelayCommand]
    public async Task PerformSearchAsync()
    {
        IsOnlineSearchEnabled = false;
        AreSearchResultsOnline = false;
        IsInSearchMode = !string.IsNullOrEmpty(SearchQuery);

        if (IsInSearchMode)
        {
            IsOnlineSearchButtonVisible = false;
        }

        await UpdateFolderPivotsAsync();
    }

    [RelayCommand]
    private async Task EnableFolderSynchronizationAsync()
    {
        if (ActiveFolder == null) return;

        foreach (var folder in ActiveFolder.HandlingFolders)
        {
            await _folderService.ChangeFolderSynchronizationStateAsync(folder.Id, true);
        }
    }

    [RelayCommand]
    private async Task LoadMoreItemsAsync()
    {
        if (IsInitializingFolder || IsOnlineSearchEnabled) return;

        await ExecuteUIThread(() => { IsInitializingFolder = true; });

        var initializationOptions = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
                                                                      SelectedFilterOption.Type,
                                                                      SelectedSortingOption.Type,
                                                                      PreferencesService.IsThreadingEnabled,
                                                                      SelectedFolderPivot.IsFocused,
                                                                      IsInSearchMode ? SearchQuery : string.Empty,
                                                                      MailCollection.MailCopyIdHashSet);

        var items = await _mailService.FetchMailsAsync(initializationOptions).ConfigureAwait(false);

        var viewModels = PrepareMailViewModels(items);

        await ExecuteUIThread(() => { MailCollection.AddRange(viewModels, clearIdCache: false); });
        await ExecuteUIThread(() => { IsInitializingFolder = false; });
    }

    #endregion

    public Task ExecuteMailOperationAsync(MailOperationPreperationRequest package) => _winoRequestDelegator.ExecuteAsync(package);

    public IEnumerable<MailItemViewModel> GetTargetMailItemViewModels(IMailItem clickedItem)
    {
        // Threat threads as a whole and include everything in the group. Except single selections outside of the thread.
        IEnumerable<MailItemViewModel> contextMailItems = null;

        if (clickedItem is ThreadMailItemViewModel clickedThreadItem)
        {
            // Clicked item is a thread.

            clickedThreadItem.IsThreadExpanded = true;
            contextMailItems = clickedThreadItem.ThreadItems.Cast<MailItemViewModel>();

            // contextMailItems = clickedThreadItem.GetMailCopies();
        }
        else if (clickedItem is MailItemViewModel clickedMailItemViewModel)
        {
            // If the clicked item is included in SelectedItems, then we need to thing them as whole.
            // If there are selected items, but clicked item is not one of them, then it's a single context menu.

            bool includedInSelectedItems = SelectedItems.Contains(clickedItem);

            if (includedInSelectedItems)
                contextMailItems = SelectedItems;
            else
                contextMailItems = [clickedMailItemViewModel];
        }

        return contextMailItems;
    }

    public IEnumerable<MailOperationMenuItem> GetAvailableMailActions(IEnumerable<IMailItem> contextMailItems)
        => _contextMenuItemService.GetMailItemContextMenuActions(contextMailItems);

    public void ChangeCustomFocusedState(IEnumerable<IMailItem> mailItems, bool isFocused)
        => mailItems.OfType<MailItemViewModel>().ForEach(a => a.IsCustomFocused = isFocused);

    private bool ShouldPreventItemAdd(IMailItem mailItem)
    {
        bool condition = mailItem.IsRead
                          && SelectedFilterOption.Type == FilterOptionType.Unread
                          || !mailItem.IsFlagged
                          && SelectedFilterOption.Type == FilterOptionType.Flagged;

        return condition;
    }

    protected override async void OnMailAdded(MailCopy addedMail)
    {
        base.OnMailAdded(addedMail);

        if (addedMail.AssignedAccount == null || addedMail.AssignedFolder == null) return;

        try
        {
            if (ActiveFolder == null) return;

            // At least one of the accounts we are listing must match with the account of the added mail.
            if (!ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == addedMail.AssignedAccount.Id)) return;

            // Messages coming to sent or draft folder must be inserted regardless of the filter.
            bool shouldPreventIgnoringFilter = addedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Draft ||
                                               addedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Sent;

            // Item does not belong to this folder and doesn't have special type to be inserted.
            if (!shouldPreventIgnoringFilter && !ActiveFolder.HandlingFolders.Any(a => a.Id == addedMail.AssignedFolder.Id)) return;

            // Item should be prevented from being added to the list due to filter.
            if (!shouldPreventIgnoringFilter && ShouldPreventItemAdd(addedMail)) return;

            await listManipulationSemepahore.WaitAsync();

            await MailCollection.AddAsync(addedMail);

            await ExecuteUIThread(() => { NotifyItemFoundState(); });
        }
        catch { }
        finally
        {
            listManipulationSemepahore.Release();
        }
    }

    protected override async void OnMailUpdated(MailCopy updatedMail)
    {
        base.OnMailUpdated(updatedMail);

        Debug.WriteLine($"Updating {updatedMail.Id}-> {updatedMail.UniqueId}");

        await MailCollection.UpdateMailCopy(updatedMail);

        await ExecuteUIThread(() => { SetupTopBarActions(); });
    }

    protected override async void OnMailRemoved(MailCopy removedMail)
    {
        base.OnMailRemoved(removedMail);

        if (removedMail.AssignedAccount == null || removedMail.AssignedFolder == null) return;

        // We should delete the items only if:
        // 1. They are deleted from the active folder.
        // 2. Deleted from draft or sent folder.
        // 3. Removal is not caused by Gmail Unread folder action.
        // Delete/sent are special folders that can list their items in other folders.

        bool removedFromActiveFolder = ActiveFolder.HandlingFolders.Any(a => a.Id == removedMail.AssignedFolder.Id);
        bool removedFromDraftOrSent = removedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Draft ||
                                      removedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Sent;

        bool isDeletedByGmailUnreadFolderAction = ActiveFolder.SpecialFolderType == SpecialFolderType.Unread &&
                                                  gmailUnreadFolderMarkedAsReadUniqueIds.Contains(removedMail.UniqueId);

        if ((removedFromActiveFolder || removedFromDraftOrSent) && !isDeletedByGmailUnreadFolderAction)
        {
            bool isDeletedMailSelected = SelectedItems.Any(a => a.MailCopy.UniqueId == removedMail.UniqueId);

            // Automatically select the next item in the list if the setting is enabled.
            MailItemViewModel nextItem = null;

            if (isDeletedMailSelected && PreferencesService.AutoSelectNextItem)
            {
                await ExecuteUIThread(() =>
                {
                    nextItem = MailCollection.GetNextItem(removedMail);
                });
            }

            // Remove the deleted item from the list.
            await MailCollection.RemoveAsync(removedMail);

            if (nextItem != null)
                WeakReferenceMessenger.Default.Send(new SelectMailItemContainerEvent(nextItem, ScrollToItem: true));
            else if (isDeletedMailSelected)
            {
                // There are no next item to select, but we removed the last item which was selected.
                // Clearing selected item will dispose rendering page.

                SelectedItems.Clear();
            }

            await ExecuteUIThread(() => { NotifyItemFoundState(); });
        }
        else if (isDeletedByGmailUnreadFolderAction)
        {
            // Remove the entry from the set so we can listen to actual deletes next time.
            gmailUnreadFolderMarkedAsReadUniqueIds.Remove(removedMail.UniqueId);
        }
    }

    protected override async void OnDraftCreated(MailCopy draftMail, MailAccount account)
    {
        base.OnDraftCreated(draftMail, account);

        try
        {
            // If the draft is created in another folder, we need to wait for that folder to be initialized.
            // Otherwise the draft mail item will be duplicated on the next add execution.
            await listManipulationSemepahore.WaitAsync();

            // Create the item. Draft folder navigation is already done at this point.
            await MailCollection.AddAsync(draftMail);

            await ExecuteUIThread(() =>
            {
                // New draft is created by user. Select the item.
                Messenger.Send(new MailItemNavigationRequested(draftMail.UniqueId, ScrollToItem: true));

                NotifyItemFoundState();
            });
        }
        finally
        {
            listManipulationSemepahore.Release();
        }
    }

    private IEnumerable<IMailItem> PrepareMailViewModels(IEnumerable<IMailItem> mailItems)
    {
        foreach (var item in mailItems)
        {
            if (item is MailCopy singleMailItem)
                yield return new MailItemViewModel(singleMailItem);
            else if (item is ThreadMailItem threadMailItem)
                yield return new ThreadMailItemViewModel(threadMailItem);
        }
    }

    [RelayCommand]
    private async Task PerformOnlineSearchAsync()
    {
        IsOnlineSearchButtonVisible = false;
        IsOnlineSearchEnabled = true;

        await InitializeFolderAsync();
    }

    private async Task InitializeFolderAsync()
    {
        if (SelectedFilterOption == null || SelectedFolderPivot == null || SelectedSortingOption == null)
            return;

        try
        {
            MailCollection.Clear();
            MailCollection.MailCopyIdHashSet.Clear();

            SelectedItems.Clear();

            if (ActiveFolder == null)
                return;

            await ExecuteUIThread(() => { IsInitializingFolder = true; });

            // Folder is changed during initialization.
            // Just cancel the existing one and wait for new initialization.

            if (!listManipulationCancellationTokenSource.IsCancellationRequested)
            {
                listManipulationCancellationTokenSource.Cancel();
            }

            listManipulationCancellationTokenSource = new CancellationTokenSource();

            var cancellationToken = listManipulationCancellationTokenSource.Token;

            await listManipulationSemepahore.WaitAsync(cancellationToken);

            // Setup MailCollection configuration.

            // Don't pass any threading strategy if disabled in settings.
            MailCollection.ThreadingStrategyProvider = PreferencesService.IsThreadingEnabled ? _threadingStrategyProvider : null;

            // TODO: This should go inside 
            MailCollection.PruneSingleNonDraftItems = ActiveFolder.SpecialFolderType == SpecialFolderType.Draft;

            // Here items are sorted and filtered.

            List<IMailItem> items = null;
            List<MailCopy> onlineSearchItems = null;

            bool isDoingSearch = !string.IsNullOrEmpty(SearchQuery);
            bool isDoingOnlineSearch = false;

            if (isDoingSearch)
            {
                isDoingOnlineSearch = PreferencesService.DefaultSearchMode == SearchMode.Online || IsOnlineSearchEnabled;

                // Perform online search.
                if (isDoingOnlineSearch)
                {
                    WinoServerResponse<OnlineSearchResult> onlineSearchResult = null;
                    string onlineSearchFailedMessage = null;

                    try
                    {
                        var accountIds = ActiveFolder.HandlingFolders.Select(a => a.MailAccountId).ToList();
                        var folders = ActiveFolder.HandlingFolders.ToList();
                        var searchRequest = new OnlineSearchRequested(accountIds, SearchQuery, folders);

                        onlineSearchResult = await _winoServerConnectionManager.GetResponseAsync<OnlineSearchResult, OnlineSearchRequested>(searchRequest, cancellationToken);

                        if (onlineSearchResult.IsSuccess)
                        {
                            await ExecuteUIThread(() => { AreSearchResultsOnline = true; });

                            onlineSearchItems = onlineSearchResult.Data.SearchResult;
                        }
                        else
                        {
                            onlineSearchFailedMessage = onlineSearchResult.Message;
                        }
                    }
                    catch (OperationCanceledException)
                    {
                        throw;
                    }
                    catch (Exception ex)
                    {
                        Log.Warning(ex, "Failed to perform online search.");
                        onlineSearchFailedMessage = ex.Message;
                    }

                    if (onlineSearchResult != null && !onlineSearchResult.IsSuccess)
                    {
                        // Query or server error.
                        var serverErrorMessage = string.Format(Translator.OnlineSearchFailed_Message, onlineSearchResult.Message);
                        _mailDialogService.InfoBarMessage(Translator.GeneralTitle_Error, serverErrorMessage, InfoBarMessageType.Warning);

                    }
                    else if (!string.IsNullOrEmpty(onlineSearchFailedMessage))
                    {
                        // Fatal error.
                        var serverErrorMessage = string.Format(Translator.OnlineSearchFailed_Message, onlineSearchFailedMessage);
                        _mailDialogService.InfoBarMessage(Translator.GeneralTitle_Error, serverErrorMessage, InfoBarMessageType.Warning);
                    }
                }
            }

            var initializationOptions = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
                                                                          SelectedFilterOption.Type,
                                                                          SelectedSortingOption.Type,
                                                                          PreferencesService.IsThreadingEnabled,
                                                                          SelectedFolderPivot.IsFocused,
                                                                          SearchQuery,
                                                                          MailCollection.MailCopyIdHashSet,
                                                                          onlineSearchItems);

            items = await _mailService.FetchMailsAsync(initializationOptions, cancellationToken).ConfigureAwait(false);

            if (!listManipulationCancellationTokenSource.IsCancellationRequested)
            {
                // Here they are already threaded if needed.
                // We don't need to insert them one by one.
                // Just create VMs and do bulk insert.

                var viewModels = PrepareMailViewModels(items);

                await ExecuteUIThread(() =>
                {
                    MailCollection.AddRange(viewModels, true);

                    if (isDoingSearch && !isDoingOnlineSearch)
                    {
                        IsOnlineSearchButtonVisible = true;
                    }
                });
            }
        }
        catch (OperationCanceledException)
        {
            Debug.WriteLine("Initialization of mails canceled.");
        }
        catch (Exception ex)
        {
            Debugger.Break();

            if (IsInSearchMode)
                Log.Error(ex, "Failed to perform search.");
            else
                Log.Error(ex, "Failed to refresh listed mails.");
        }
        finally
        {
            listManipulationSemepahore.Release();

            await ExecuteUIThread(() =>
            {
                IsInitializingFolder = false;

                OnPropertyChanged(nameof(CanSynchronize));
                NotifyItemFoundState();
            });
        }
    }

    #region Receivers

    void IRecipient<MailItemSelectedEvent>.Receive(MailItemSelectedEvent message)
    {
        if (!SelectedItems.Contains(message.SelectedMailItem)) SelectedItems.Add(message.SelectedMailItem);
    }

    void IRecipient<MailItemSelectionRemovedEvent>.Receive(MailItemSelectionRemovedEvent message)
    {
        if (SelectedItems.Contains(message.RemovedMailItem)) SelectedItems.Remove(message.RemovedMailItem);
    }

    async void IRecipient<ActiveMailFolderChangedEvent>.Receive(ActiveMailFolderChangedEvent message)
    {
        NotifyItemSelected();

        isChangingFolder = true;

        ActiveFolder = message.BaseFolderMenuItem;
        gmailUnreadFolderMarkedAsReadUniqueIds.Clear();

        trackingSynchronizationId = null;
        completedTrackingSynchronizationCount = 0;

        // Notify change for archive-unarchive app bar button.
        OnPropertyChanged(nameof(IsArchiveSpecialFolder));

        IsInSearchMode = false;
        IsOnlineSearchButtonVisible = false;
        AreSearchResultsOnline = false;

        // Prepare Focused - Other or folder name tabs.
        await UpdateFolderPivotsAsync();

        // Reset filters and sorting options.
        ResetFilters();

        await InitializeFolderAsync();

        // TODO: This should be done in a better way.
        while (IsInitializingFolder)
        {
            await Task.Delay(100);
        }

        // Check whether the account synchronizer that this folder belongs to is already in synchronization.
        await CheckIfAccountIsSynchronizingAsync();

        // Let awaiters know about the completion of mail init.
        message.FolderInitLoadAwaitTask?.TrySetResult(true);

        await Task.Yield();

        isChangingFolder = false;

        void ResetFilters()
        {
            // Expected that FilterOptions and SortingOptions have default value in 0 index.
            SelectedFilterOption = FilterOptions[0];
            SelectedSortingOption = SortingOptions[0];
            SearchQuery = string.Empty;
            IsInSearchMode = false;
            IsOnlineSearchEnabled = false;
        }
    }

    public void Receive(AccountSynchronizationCompleted message)
    {
        if (ActiveFolder == null) return;

        bool isLinkedInboxSyncResult = message.SynchronizationTrackingId == trackingSynchronizationId;

        if (isLinkedInboxSyncResult)
        {
            var isCompletedAccountListed = ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == message.AccountId);

            if (isCompletedAccountListed) completedTrackingSynchronizationCount++;

            // Group sync is started but not all folders are synchronized yet. Don't report progress.
            if (completedTrackingSynchronizationCount < ActiveFolder.HandlingFolders.Count()) return;
        }

        bool isReportingActiveAccountResult = ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == message.AccountId);

        if (!isReportingActiveAccountResult) return;

        // At this point either all folders or a single folder sync is completed.
        switch (message.Result)
        {
            case SynchronizationCompletedState.Success:
                UpdateBarMessage(InfoBarMessageType.Success, ActiveFolder.FolderName, Translator.SynchronizationFolderReport_Success);
                break;
            case SynchronizationCompletedState.Failed:
                UpdateBarMessage(InfoBarMessageType.Error, ActiveFolder.FolderName, Translator.SynchronizationFolderReport_Failed);
                break;
            default:
                break;
        }
    }

    void IRecipient<MailItemNavigationRequested>.Receive(MailItemNavigationRequested message)
    {
        Debug.WriteLine($"Mail item navigation requested");
        // Find mail item and add to selected items.

        MailItemViewModel navigatingMailItem = null;
        ThreadMailItemViewModel threadMailItemViewModel = null;

        for (int i = 0; i < 3; i++)
        {
            var mailContainer = MailCollection.GetMailItemContainer(message.UniqueMailId);

            if (mailContainer != null)
            {
                navigatingMailItem = mailContainer.ItemViewModel;
                threadMailItemViewModel = mailContainer.ThreadViewModel;

                break;
            }
        }

        if (threadMailItemViewModel != null)
            threadMailItemViewModel.IsThreadExpanded = true;

        if (navigatingMailItem != null)
            WeakReferenceMessenger.Default.Send(new SelectMailItemContainerEvent(navigatingMailItem, message.ScrollToItem));
    }

    #endregion

    public async void Receive(NewMailSynchronizationRequested message)
        => await ExecuteUIThread(() => { OnPropertyChanged(nameof(CanSynchronize)); });

    protected override async void OnFolderSynchronizationEnabled(IMailItemFolder mailItemFolder)
    {
        if (ActiveFolder?.EntityId != mailItemFolder.Id) return;

        await ExecuteUIThread(() =>
        {
            ActiveFolder.UpdateFolder(mailItemFolder);

            OnPropertyChanged(nameof(CanSynchronize));
            OnPropertyChanged(nameof(IsFolderSynchronizationEnabled));
        });

        SyncFolderCommand?.Execute(null);
    }

    public async void Receive(AccountSynchronizerStateChanged message)
        => await CheckIfAccountIsSynchronizingAsync();

    private async Task CheckIfAccountIsSynchronizingAsync()
    {
        bool isAnyAccountSynchronizing = false;

        // Check each account that this page is listing folders from.
        // If any of the synchronizers are synchronizing, we disable sync.

        if (ActiveFolder != null)
        {
            var accountIds = ActiveFolder.HandlingFolders.Select(a => a.MailAccountId);

            foreach (var accountId in accountIds)
            {
                var serverResponse = await _winoServerConnectionManager.GetResponseAsync<bool, SynchronizationExistenceCheckRequest>(new SynchronizationExistenceCheckRequest(accountId));

                if (serverResponse.IsSuccess && serverResponse.Data == true)
                {
                    isAnyAccountSynchronizing = true;
                    break;
                }
            }
        }

        await ExecuteUIThread(() => { IsAccountSynchronizerInSynchronization = isAnyAccountSynchronizing; });
    }

    public void Receive(AccountCacheResetMessage message)
    {
        if (message.Reason == AccountCacheResetReason.ExpiredCache &&
            ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == message.AccountId))
        {
            var handlingFolder = ActiveFolder.HandlingFolders.FirstOrDefault(a => a.MailAccountId == message.AccountId);

            if (handlingFolder == null) return;

            _ = ExecuteUIThread(() =>
            {
                MailCollection.Clear();

                _mailDialogService.InfoBarMessage(Translator.AccountCacheReset_Title, Translator.AccountCacheReset_Message, InfoBarMessageType.Warning);
            });
        }
    }

    public void Receive(ThumbnailAdded message) => MailCollection.UpdateThumbnails(message.Email);
}
